I have really only been concerned about Push Mail to my iPhone (and Contacts and Calendar). However, after reading posts about Push Mail to Mail.app now working I decided to test with Outlook and Window Live Desktop (It has been working but I did not think it was Push). Too my suprise it is instant. I sent email to myself (userid@me.com) and it would hit MM Web Interface, Outllook 2007, Windows Live Desktop (IMAP) and my iPhone at the same time within 1 second. I did this test about 5 times over a period of 5 min and it was the same.